Why has Prince Prospero locked himself and his guests in the abbey in "The Masque of the Red Death"?

Prince Prospero is trying to escape a deadly plague that is running rampant through his country.  Anyone who becomes infected with the "red death" begins to bleed from all pores and dies within thirty minutes.  Prospero gathers one thousand of his people, and they seal themselves in the abbey to wait for the plague to be over.  His name, "Prospero", is ironic because he does not prosper by locking himself away; no one can escape death.